💡When Keratin Misleads: Keratotic BCC Mimicking PTT! A 51-year-old man with a longstanding sun-exposed scalp lesion developed recent discharge. Histology showed a prominent nodular, basaloid to squamous proliferation with keratin-filled cystic structures, creating a challenging differential: 🔹 Keratotic BCC 🔹 SCC with follicular differentiation 🔹 Proliferating trichilemmal tumour (PTT) – benign/malignant Interestingly, SCC with follicular differentiation received the maximum votes, followed by malignant PTT. Keratotic BCC was not the leading choice — and I had the same dilemma initially! 🧩 The diagnostic clue: IHC BerEP4: diffuse, strong positivity → strongly supports BCC and argues against conventional SCC and PTT. BCL2: diffuse positivity → supportive of BCC. EMA: negative → favours BCC over SCC. CD34: Negative in tumor cells - favors BCC over PTT 🎯 The take-home point Don’t be fooled by the keratin! Keratotic BCC can show prominent squamous/follicular differentiation and closely mimic SCC or PTT. 👉 Look carefully for the underlying BCC architecture and use BerEP4 as a valuable adjunct when morphology is equivocal. Final diagnosis: KERATOTIC BASAL CELL CARCINOMA. Sometimes the most difficult cases are those where the morphology makes you believe the wrong diagnosis first! 😉 #Dermatopathology #KeratoticBCC #BasalCellCarcinoma #ProliferatingTrichilemmalTumor #SCC #Histopathology #Pathtwitter